1. Field of the Invention
The present invention relates to an inspection probe including probe pins having electric contacts that come into contact with electrodes (pad or bump) of a large scale integration (LSI) chip or a bear LSI chip (bear chip) (i.e., a semiconductor device). More specifically, the present invention relates to an inspection probe including probe pins having electric contacts suitable for inspecting an LSI chip or a bear chip including electrodes having oxidation films and having a small electrode pitch. Moreover, the present invention relates to a method for preparing the inspection probe and a method for inspecting elements.
2. Description of the Related Art
A known inspection probe conducts an inspection of a semiconductor device by bringing probes provided on an inspection substrate into contact with the external terminal electrodes of the semiconductor device to be inspected and electrically connecting the semiconductor device and the inspection substrate. The probe pins may be metal leads attached to a flexible substrate, metal leads attached to a rigid base substrate, pins prepared by plating silicon whiskers or metal pins. Three different types of inspection probes have been proposed: a membrane sheet including metal leads (tape automated bonding (TAB)), metal leads attached to a rigid base substrate, and silicon whiskers. These different structures will be described below.
(1) A Probe Using a Membrane Sheet Including Metal Leads (TAB)
This type of probe includes those disclosed in JP-A-6 334006, JP-A-6 334005, JP-A-6 331655, and JP-A-6 324081. The probes described in these documents are structured so that metal leads provided on a flexible substrate oppose external electrodes of the semiconductor device to be inspected. FIGS. 1A and 1B illustrate the probe card disclosed in JP-A-6 334006 as a typical example of this type of probe. A predetermined inspection circuit pattern and probe pins 1 are provided on one side of a flexible film 30 of the probe card illustrated in FIG. 1. The probe pins 1 come into contact with external electrodes of a semiconductor device 10.
The probe pins 1 cannot obtain the desired amount of contact when using only a flexible substrate 7 because the flexible substrate 7 is thin. Therefore, a clamper 32 and a support 36 are provided to support both sides of the flexible substrate 7. In this way, the desired amount of contact by the probe pins 1 can be obtained. The clamper 32, the flexible substrate 7, the film 30, an insulating sheet 31, a print substrate 34, and a reinforcement plate 35 are fixed to the support 36 with a plurality of bolts 33.
(2) A Probe Using Metal Leads Attached to a Rigid Base Substrate
This type of probe includes those disclosed in JP-A-2002 286755, JP-A-2002 286758, and JP-A-2003 185674. The probes described in these documents are structured so that metal leads provided on a rigid base substrate oppose external electrode of the semiconductor device to be inspected. The structural views of FIGS. 2A, 2B and 3 illustrate the probe units and the method for preparing the probe units disclosed in JP-A-2002 286758 and JP-A-2003 185674 as a typical example of this type of probe. FIGS. 2A and 2B illustrate the entire structure of the probe unit. The probe unit comprises a rigid base substrate 2 that may be composed of glass, synthetic resin, ceramic, silicon laminated with an insulating material, or metal (according to the column 4, lines 40 to 44 of JP-A-2003 121466). On one side of the rigid base substrate 2, leads 3 and arc-shaped probe pins 1 are provided, or instead, the leads 3, the arc-shaped probe pins 1, and protrusions 39 are provided. The probe pins 1 come into contact with the external electrodes of the semiconductor device. A metal piece 37 is passed through a communication hole 38 formed on the rigid base substrate 2.
The probe pins 1 are resilient and are capable of contacting the electrodes of the semiconductor device with a predetermined amount of penetration and load within an elastic deformation region.
FIG. 3 illustrates the shapes of the tips of the probe pins that come into contact with the electrodes of the semiconductor device. The tips of the probe pins comprise steepled or knife-edge protrusions 41, 43, and 45 provided at the tips of the probe pins and supports 40, 42, and 44.
(3) A Probe Using Silicon Whiskers
This type of probe includes those disclosed in JP-A-10 038918, JP-A-2002 257859, and JP-A-5 198636. FIG. 9 is a structural view illustrating a probe pin and a contactor including the probe pin as a typical example of this type of probe disclosed in JP-A-10 038918. According to this document, probe pins 1 are prepared by growing silicon needle crystals 53 and covering the needle crystals with a nickel base film 54 and then with a gold film. On the gold film at the tips of the needle crystals, a palladium film 56 is provided. The silicon needle crystals 53 are grown by a vapor-liquid-solid (VLS) crystal growth method by placing a gold seeds for growing the crystals on a silicon substrate 52. The probe pins 1 according to this document have a conductive film provided on the surfaces and are used for semiconductor measurements. Only the tips of the probe pins 1 are covered with a conductive material.
(4) A Probe Using Metal Pins
The probe device disclosed in JP-A-6 140482 is illustrated in FIGS. 10A and 10B. The probe device comprises extremely fine wire probe needles 57 prepared by processing metal pins, such as tungsten pins, and crystal probe needles 60. The probe device has a short electrode pitch but can be provided at low cost. For example, to prepare this probe device, the tungsten wire probe needles 57 and the crystal probe needles 60 are provide on a printed circuit board 34 wherein the tungsten wire probe needles 57 are provided in areas where the electrode pitch is wide (300 to 400 μm) and the crystal probe needles 60 are provided in areas where the electrode pitch is narrow (45 to 65 μm). The crystal probe needles 60 are prepared by forming electrode patterns by etching the tip of a crystal plate 58 and plating the surface with gold. Since the crystal probe needles 60 are used, the electrode pitch may be reduced to a very fine pitch level of 40 μm. By using different probes in areas having different electrode pitches, the production cost of the probe device is reduced compared to the production cost for a probe device that includes only crystal probes. The wire probe needles 57 are supported on the printed circuit board 34 so that they protrude into a window 59 formed on the printed circuit board 34. The crystal probe needles 60 are disposed on a flexible substrate 7 so that they protrude into the window 59 formed on the printed circuit board 34. The flexible substrate 7 is supported on the printed circuit board 34 and is connected with a contact pin 61 on the printed circuit board 34. The printed circuit board 34 includes an X-axis bolt 33a, a Z-axis bolt 33b, a θ-axis bolt 33c, and a Y-axis adjuster 62.
The probe unit disclosed in JP-A-2003 207521 comprises probe pins and a probe support including an inorganic insulating layer, and a base metal layer.
The probe pins of a probe unit disclosed in JP-A-2003 322664 are provided as part of lead patterns formed on the surface of the substrate by lithography.
Since the probe card disclosed in JP-A-6 334006 includes a flexible film as a substrate, the following problems exist: 1) it is difficult to control the positional accuracy in the pitch direction of the metal leads at a predetermined value (±1.0 μm or less) when the pitch is 40 μm or less, due to the thermal history of the film substrate preparation process; 2) the metal lead and the electrode of the semiconductor device are misaligned when a high-temperature inspection of 80 to 100° C. is carried out on the wafer, because the thermal expansion coefficient of the film material (several tens of ppm) is greater than the thermal expansion coefficient of the silicon of the semiconductor (2 to 3 ppm); and 3) it is difficult to obtain good contact between probe pins and the semiconductor electrode when the probe pins are composed of a single metal material having elasticity and the semiconductor electrode is composed of a material having an oxidation film of aluminum or copper.
The probe unit and the method for preparing the probe unit disclosed in JP-A-2002 286758 use a glass plate, a synthetic resin plate, a ceramic plate, a silicon plate covered with an insulating material, or a metal plate for a substrate. Since the thermal expansion coefficient except for a synthetic resin is relatively similar to silicon, the reduction of the accuracy due to the thermal history during manufacturing and the displacement during a high-temperature test are extremely small and do not cause any problems. Thus, this probe unit solves the first and second problems of the probe card according to JP-A-6 334006.
Even if the semiconductor electrode comprises an oxidation film, the oxidation film can be penetrated by the protrusions formed on the top of the arcs according to JP-A-2002 286758 and the steepled protrusions or the knife-edge protrusions according to JP-A-2003 185674.
However, to penetrate the oxidation film, the steepled protrusions or the knife-edge protrusions must have a radius of curvature smaller than a predetermined value. Especially, when the pitch of the semiconductor electrodes is reduced to 40 μm or less, the size of the probe pins has to be reduced. For this reason, the amount of overdrive (penetration amount of the probe into the electrode) that does not cause the probe pins to elastically deform is reduced. Thus, the amount of force that can be applied to the contact areas becomes significantly small. Accordingly, the following problems exist: 1) the production cost of the probe pins increases significantly compared to other known probe pins to satisfy the requirements for the radius of curvature; and 2) elastic deformation occurs due to concentration of stress during contact at the base of the area where a steepled protrusion or a knife-edge protrusion is formed on the tip of the knife-edge area of the probe pin because the thickness of this area is thinner than the other areas. These problems will be described in detail below.
FIGS. 4A and 4B are views showing the tips of probe pins having a pitch of 20 μm. A pitch expansion wiring layer 3 of probe pins 1 is provided on a base substrate 2. A flexible substrate 7 is connected to the base substrate 2. A knife-edge portion 46 is formed on the tip of a thin portion 47 of each of the probe pins 1.
FIGS. 5A and 5B illustrate the measurement results of the contact characteristics of the probe pins 1. All probe pins become conductive when an overdrive of 50 μm or more is applied. However, among these probe pins, there are areas that are highly resistive. FIG. 6 illustrates a tip 48 of the probe pin 1 causing a scrub mark (a low-resistance area 50) on an electrode of a semiconductor device 10 and a tip 49 of the probe pin 1 causing a scrub mark (a high-resistance area 51) on the electrode. Where a high-resistance area occurs, the tip 49 of the probe pin 1 becomes round. Consequently, the probe pin 1 slips on the surface of the electrode, the oxidation film interposed between the surface of the electrode and the probe pin 1 at the contact area is not penetrated by the probe pin 1. To solve this problem, the knife-edge protrusion must be adjusted so that the radius of the tip is 0.36 μm or less, which is the same level as the low-resistance area 50. FIG. 7 is a view showing the vicinity of the tip of the probe pin 1 and the dimensions of the probe pin 1. FIG. 8 is a view showing the contact condition of the probe pin 1. As shown in FIG. 7, a thin area exists between the knife-edge area and the base material of the probe pin 1 and deformation occurs from the base of this thin area. As a result of several contacts made between the electrode and the probe pin, the thin area becomes elastically deformed and causes the probe pin 1 to malfunction. The length of the thin area can be shortened by improving the processing carried out before the knife-edge area is formed. However, it is impossible to reduce the length of the thin area to zero. Moreover, the production cost will be significantly increased if the length of the thin area is minimized.
The above-described two problems can be easily and clearly understood through the above-described examples according to JP-A-2002 286758 and JP-A-2003 185674.
JP-A-10 038918 discloses a structure in which probe pins prepared by plating needle crystals contact external electrodes of a semiconductor device. Because of this structure, when pins having a diameter of about 10 μm, which is suitable for an electrode pitch of 20 μm (the pitch should be 40 μm or less), it becomes extremely difficult to dispose a gold bump onto a silicon mesa before growing the pins and damage occurs because of stress caused when a metal film is applied and when the tips of the pins are trimmed after the pins are formed. Therefore, due to these reasons, the following problems occur: 1) it is difficult to maintain the positional accuracy corresponding to the electrode pitch of the semiconductor device; 2) the pins break when an overdrive is applied because the pins are extremely fine and have an exceptionally small diameter and thus lack strength; and 3) the production cost is high because a metal film is applied over the entire silicon pin and another metal film is applied to the tip of the pin to provide conductivity.
According to the structure disclosed in JP-A-6 140482, either tungsten wire probe pins or crystal probes are used to contact external electrodes of a semiconductor device in accordance with the magnitude of the electrode pitch. Because of this structure, the diameter of the wire probe pins has to be 20 μm or less for areas having a small electrode pitch of 40 μm or less. Therefore, the following problems occur: 1) it is extremely difficult to manufacture the probe pins, and even if the probe pins are manufactured successfully, it is extremely difficult to align them accurately and the probe pins lack durability; 2) it is difficult to maintain positional accuracy with respect to the electrode pitch of the semiconductor device of the crystal probes because of the stress generated when a metal film is applied to the crystal probes, which is a problem similar to the silicon pins according to JP-A-10 038918; 3) the pins break when an overdrive is applied because the pins are extremely fine with an exceptionally small diameter and lack strength; 4) the production cost is high when only crystal probes are used; and 5) the pins are not durable enough to be used at a practical level even when the overdrive applied does not cause the pins to break, which is a problem similar to that in JP-A-10 038918.